The present invention relates to an optical waveguide and a thermally-assisted magnetic recording head with the optical waveguide.
In the field of magnetic recording using a head and a medium, further improvements have been demanded in performance of thin film magnetic heads and magnetic recording media in view of an increase in recording density of magnetic disk devices. For the thin film magnetic heads, composite type thin film magnetic heads formed by lamination of a reading magnetoresistive (MR) element and a writing electromagnetic conversion element are being widely used.
In contrast, the magnetic recording medium is a so-called non-continuous medium, in which magnetic particles are aggregated. Each magnetic particle has a single magnetic domain. Here, a single recording bit is formed by a plurality of magnetic particles. Therefore, to increase magnetic density, the size of the magnetic particles must be reduced, and asperity at a border of recording bits needs to be minimized. However, if the size of the magnetic particles is reduced, there is a problem that thermal stability for magnetization of the magnetic particles is lowered as the volume of the magnetic particles is reduced.
To address this problem, increasing magnetic anisotropic energy Ku of magnetic particles may be considered. However, this increase in Ku causes an increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. On the other hand, the upper limit of the writing magnetic field intensity for the thin film magnetic head is determined substantially by a saturation magnetic flux density of a soft magnetic material forming a magnetic core in the head. As a result, when the anisotropic magnetic field of the magnetic recording medium exceeds an acceptable value determined from the upper value of the writing magnetic field intensity, writing becomes impossible. Currently, as a method to solve such a problem of thermal stability, a so-called thermally-assisted magnetic recording method has been proposed, which uses a magnetic material with a large Ku, which also performs the writing by heating the magnetic recording medium immediately before applying the writing magnetic field to reduce the anisotropic magnetic field.
For this thermally-assisted magnetic recording method, a method that uses a near-field probe, a so-called plasmon antenna, is known. The near-field probe is a piece of metal that generates near-field light from plasmon excited by irradiated laser light. For example, a plasmon generator that includes a metal scatterer having a shape of a cone or the like formed on a substrate is disclosed in U.S. Pat. No. 6,768,556.
In addition, a configuration is disclosed in U.S. Patent Publication No. 2004/081031 A1, in which a plasmon generator is formed at a position to contact the main magnetic pole of a perpendicular magnetic recording head so that an irradiated surface of the plasmon generator is perpendicular to the magnetic recording medium. Moreover, U.S. Patent Publication No. 2003/066944 A1 discloses a technology, in which irradiation of stronger near-field light onto the magnetic recording medium is attempted by preferentially positioning the front end of a plasmon antenna close to the magnetic recording medium.
The inventors of the present application have considered the potentiality of the magnetic recording by irradiation of the near-field light to be a breaking point and have been developing more improved thermally-assisted magnetic recording heads.
For performing the thermally-assisted recording by the irradiation of the near-field light with a magnetic recording head, it is necessary to install a laser light generating device, which is a light emitting element, in the magnetic recording head, to take in laser light emitted from the laser light generating device into an optical waveguide, and to guide the laser light to a plasmon antenna located near a position opposing the magnetic recording medium.
There are techniques for taking in the laser light emitted from the laser light generating device by providing a grating on a plane on one side of the optical waveguide and for optically coupling the laser light with the optical waveguide through the grating and subsequently for letting the laser light propagate in the optical waveguide (e.g., U.S. Pat. No. 6,944,112 and Nature Photonics (Seagate) Mar. 22, 2009).
The technique disclosed in U.S. Pat. No. 6,944,112 irradiates the laser light emitted from the laser light generating device not perpendicularly, but diagonally, to a diffraction grating formed on a planar waveguide. In addition, the external shape of the planar waveguide is a parabolic shape, which is different from a shape of a spot size converter that focuses the laser light in a single mode. According to the technique disclosed in U.S. Pat. No. 6,944,112, the light that has propagated is once reflected in a part of the parabolic shape and is collected at the focal point.
Moreover, the technique disclosed in Nature Photonics (Seagate) is similar to U.S. Pat. No. 6,944,112. The external shape of the planar waveguide is a parabolic shape and is not a shape of a spot size converter that focuses the laser light in a single mode. Therefore, the laser light is once reflected in a part of the parabolic shape and is collected at the focal point. Further, in this document, the planar waveguide includes a dual offset grating, in which two gratings are arranged in parallel with each other. As a result, because the laser light reflected in parts of the parabolic shape intersects with each other at the focal point, final polarization (oscillation) of light is in the same up-down direction as presented on a sheet. Therefore, there is a problem that the laser light is not efficiently coupled with an element that uses the surface plasmon, on which the light propagates towards an air bearing surface (ABS).
An object of the present invention is to provide a configuration in which the laser light is reliably optically coupled with the optical waveguide by the laser light incident perpendicularly onto the optical waveguide, and an optical waveguide through which the laser light is subject to propagate in a target direction. To achieve the object, a positional relationship between the optical waveguide and the laser light generating device is simplified so that the laser light generating device is easily installed.